In our copending United Kingdom Patent Application No. 8626685 (UK-A-2183200) we have described a method for producing hollow cored construction products from dry particulate material wherein there is proposed an additional step in the process involving the application of pressure to damp, uncured material while it is in the mould, the pressure being applied from within the material by an expandable sleeve positioned within each core void.
A typical construction product made by the method comprises a building panel having a plurality of parallel core voids extending the full vertical extent thereof, such voids being formed by expandable core void formers positioned in the mould. The mould is filled, whilst being vibrated, with an appropriate dry powder mix, optimally containing fibres, such vibration imparting an initial or pre-compaction to the mix. After such pre-compaction, the core void formers are expanded to apply pressure to and thereby further compact the mix and are then retracted to their pre-expanded state to allow them to be withdrawn, leaving corresponding core voids in the compacted dry powder mix. The powder surfaces of the voids are then lightly sprayed with setting liquid and, after sufficient liquid has been absorbed, a further set of expandable core void formers (called hereinafter "reblow formers") are inserted into the voids and expanded in order to press the dampened material firmly to the mould sides in order to ensure a good quality surface finish to the final moulded product.